In the conventional shoulder-aimed firearm, which is the most accurate of the hand-carried weapons, the barrel is mounted upon a stock which extends rearwardly to rest against the shooter's shoulder as a shoulder stock. When the weapon is in firing position, the shoulder stock is against the shoulder and the eye is on the line-of-sight which is directly above the barrel. The sights by which the firearm is aimed are normally mounted upon the barrel and/or receiver. By careful aim, such hand-carried weapons can accurately place a bullet.
A problem of such weapons was encountered in World War I when they were used in trench warfare. The shooter's head was exposed when he was aiming his weapon. Several patents were granted which disclosed the use of a prism mounted behind the rear sight in such a manner that the prism permits a view down the line-of-sight from a right angle position beside the weapon. Such prisms did not permit accurate shooting because the weapon could not permit accurate shooting because the weapon could not be securely held and the sighting view was unnatural.
Periscopes were also available in trench warfare, and such periscopes were semi-permanently attached to the shoulder-aimed firearm. Difficulties arose because the firearm was not capable of being used by direct sighting down the line-of-sight because such structures were not provided so as to be able to quickly and easily remove the periscope from obstructing the direct line-of-sight. Thus, there is need for a handcarried weapon which permits the shooter to remain in a protected position while the barrel of the weapon can be directed at a target and properly held during shooting.